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ACIP Reaffirms Recommendation for Annual Influenza Vaccination

Feb 26, 2015

Today the Advisory Committee on Immunization Practices (ACIP) voted on its annual influenza vaccine recommendations for 2015-2016. ACIP voted to continue to recommend that all persons 6 months and older be vaccinated annually against influenza. However ACIP did not renew the 2014-2015 preference for using the nasal spray flu vaccine (i.e., LAIV) instead of the flu shot (i.e., IIV) in healthy children 2 through 8 years of age when immediately available. The preferential recommendation was originally approved on June 25, 2014, after a review of data from several influenza seasons suggested that the nasal spray vaccine could offer better protection than the flu shot for children in this age group. The decision not to renew the preferential recommendation was made based on new data from more recent seasons which have not confirmed superior effectiveness of LAIV observed in earlier studies. ACIP recommends that children 6 months and older get an annual influenza vaccine with no preference stated for either the nasal spray vaccine or the flu shot.

ACIP is a panel of immunization experts that advises the Centers for Disease Control and Prevention (CDC). Part of the ACIP charter is to continually evaluate new data and update or change recommendations as warranted. The new data considered by ACIP included vaccine effectiveness (VE) estimates for 2013-2014 and for the current 2014-2015 season.

2013-2014: On October 29, 2014, VE data for the 2013-2014 season were presented to ACIP. These data showed no measurable effectiveness for LAIV against influenza A (H1N1) among children while the IIV vaccine effectiveness mid-point estimate against H1N1 in children 2 through 8 years that season was 60% and was statistically significant. H1N1 was the predominant virus in circulation during the 2013-2014 season for the first time since it emerged in 2009 to cause a pandemic.

2014-2015: Today, interim data from the U.S. Flu VE Network was presented to ACIP. The mid-point vaccine effectiveness estimate for IIV against H3N2 in children ages 2 through 8 years was 15% (95% confidence interval of -20 to 40) and for LAIV it was -23% (95% confidence interval of -90 to 21) These data suggest that neither vaccine worked well in protecting against H3N2 viruses this season, and that LAIV did not work better than IIV against the predominant H3N2 viruses circulating during the current season. Limited data are available on LAIV effectiveness against drifted H3N2 viruses, but some past studies had suggested that LAIV might offer better protection against such viruses.(1)

Since 2010, CDC and ACIP have recommended that everyone 6 months and older get a flu vaccine annually with rare exception. Although flu vaccine is the best way to prevent influenza infection, how well it works can vary. Since CDC began measuring vaccine effectiveness in 2004-2005, estimates have ranged from 10% to 60%. One factor that can influence how well the vaccine works is the similarity between the vaccine viruses and circulating influenza viruses. More than two-thirds of the H3N2 viruses circulating nationally in the U.S. this season are different from the H3N2 vaccine virus; the proportion of drifted viruses is higher (>80%) at the U.S. VE Network study sites. Host factors of the person being vaccinated like age, health and immune status also can impact how well the vaccine works.

The ACIP recommendation must be adopted by the CDC director. The recommendation would then be incorporated into the 2015-2016 influenza prevention and control recommendations and published in a Morbidity and Mortality Weekly Report (MMWR), at which point it would become official CDC policy.

Reference: 1. Two of five randomized control trials (RCTs) conducted during seasons when drifted H3N2 viruses circulated reported good protection by LAIV against those viruses and one suggested LAIV offered more protection that IIV.